The present invention is a system for determining whether an eye within a field of view is closed for a predetermined period of time and for distinguishing between an open eye and any specular reflectors within the field of view. Although the present invention is disclosed as part of an alertness monitor system, it is not limited to such applications.
In manufacturing environments requiring the use of heavy machinery in dark or dimly lit areas, for example, in the confines of a mine it is useful to provide a system to monitor and maintain driver alertness. Ideally, such a system might consist of a device which sets off an alarm when the subject closes his eyes for a period greater than some predetermined length of time. Such a system might also be used for a variety of commercial applications, for example, as a remote eye-controlled switch.
The operational object of an alertness monitor is to detect and distinguish the presence of an open eye in some specific field of view and to discriminate between eye blinks and the condition of sleep. A prior art eye fundus camera described in U.S. Pat. No. 4,149,787 provides a means to detect eye closure. However, unlike the present invention, it requires proximity of the eye to the device, only provides a limited field of view, and does not have provision to discriminate between the eye and other bright objects within that field of view. In addition, also unlike the present invention, it relies on the principle that under certain forms of illumination the eye lid will reflect more light than the eye itself.
In addition, there are many prior art systems which track eye motion or relate the line of sight of the eye to some coordinate system. In one such device, an oculometer described in U.S. Pat. No. 3,462,604, a source is used to illuminate an area which contains the subject's head. The light reflected off the back surface of the eye through the pupil creates a bright spot, much like a cat's-eye retroreflector. If a television camera or other imaging device is placed along the boresight of the source to record scene illumination, the location of the bright spot, in relation to other reflections off the eye, can be used to determined the line of sight of the eyes.
In the embodiment disclosed, the present invention uses a variation of this optical technique, termed bright pupil illumination, to remotely determine eye presence. Briefly, the disclosed system uses a pair of switched sources to provide consecutive pairs of images with and without bright pupil illumination by which the subject's eyes can be distinguished from self-luminous objects or specular reflections off glasses or other objects in the scene. An alarm is set off when the subject closes his eyes longer than a predetermined length of time.